I'm only familiar with the cost-share incentives here in Illinois -- you'll have to visit other states' forestry websites for their forestry cost-share offerings.
Illinois' flagship forestry program that guarantees the lowest possible property tax assessment is the Forestry Development Act (FDA):
Another option is the state's version of the Conservation Stewardship Program (CSP):
Illinois also offers a nice suite of federal USDA Farm Bill conservation program offerings for tree planting / forestry with the following two programs being the most popular: Environmental Quality Incentives Program (EQIP) and the Conservation Reserve Program (CRP). To enroll in these programs, a producer needs to visit their county USDA Farm Service Agency office.